1. Field of the Invention
This invention relates to lubricant compositions, and relates more particularly to lubricant compositions normally subject to degradation by ultra-violet light present in for example such sources of actinic radiation as sunlight. Still more particularly, the invention relates to lubricant compositions, such as oils of lubricating viscosity, e.g., hydrocracked lubricating oils, hydraulic oils, automotive oils, gear oils, transmission fluids, waxes, greases and other forms of lubricants normally requiring the presence of stabilizing agents against the degradative effects of ultra-violet light.
2. Description of the Prior Art
In general, the production of lubricant compositions, for example, lubricating oils produced by hydrocracking affords a relatively high viscosity index and permits the use of certain stocks that would be unsuitable for other processes. On the other hand, however, hydrocracked lubricating oils tend toward poor stability against ultra-violet light degradation, rapidly forming suspended and/or precipitated insoluble material on exposure to ultra-violet light, such as sunlight, or other sources of actinic radiation. Compounds capable of absorbing ultra-violet light, for example, hydroxybenzophenones and hydroxyphenyl benzotriazoles, have afforded some improvement in the light stability of hydrocracked oils. Conventional antioxidants have also provided some benefit.
In the literature, Heskins and Guillet in "Mechanism of Ultraviolet Stabilization of Polymers", Macromolecules 1, 97 (1968), first proposed the energy transfer mechanism of ultra-violet protection. Commercially available ultra-violet stabilizers are also listed by class and function and identified as to structure in the Kirk-Othmer Encyclopedia in "Encyclopedia of Chemical Technology"; Second Edition, Vol. 21, pp. 115-122. Uri in "Thermal and Photochemical Oxidation of Polymers and Its Prevention", Chemistry and Industry, Mar. 1, 1975, pp. 199-203, cites conventional antioxidant effects (hydroperoxide decomposition and free radical capture) of bis (stilbenedithiolato) nickel and its ultra-violet inhibiting properties. In British Patent Specification No. 1,263,910 (1972), there is disclosed bis (stilbenedithiolato) nickel as an antioxidant for plastic materials. The specification also cites the superior hydroperoxide decomposition capability of this additive. U.S. Pat. No. 3,832,304, discloses the use of aromatic azo compounds for stabilizing hydrocracked oils. Additionally in the patent literature, for example, U.S. Pat. Nos. 3,149,077; 3,448,662; 3,450,636 and 3,654,329 disclose the use of nickel salts complexed with dithiophosphorous compounds as being useful in lube oils and functional fluids. Further, U.S. Pat. Nos. 2,703,786; 2,716,090 and 3,210,277 disclose the use of polyvalent (e.g. Ni) metal salts of alkyl phenol sulfides as oxidation inhibitors and plasticizing agents. Various other polyvalent metal (e.g. nickel) compounds are disclosed in the patent literature, for example U.S. Pat. No. 3,630,897 discloses metal salts (e.g. nickel, iron, zinc) of substituted dithiocarbamic acids and U.S. Pat. No. 3,252,910 discloses compounds such as nickel N,N-substituted dithiooxamides. U.S. Pat. Nos. 2,971,940 and 2,971,941 disclose nickel phenol-phenolate complexes as being useful in stabilizing polyethylene and polypropylene. U.S. Pat. Nos. 3,215,717 and 3,313,770 disclose certain nickel amine sulfide complexes as being useful for stabilizing various polyolefinic plastic materials. To the best of applicants' knowledge the lubricant compositions containing the nickel complexes described herein have not heretofore been disclosed.